EP1011264A1

EP1011264A1 - Contour emphasizing circuit

Info

Publication number: EP1011264A1
Application number: EP98933928A
Authority: EP
Inventors: Toru Fujitsu General Limited AIDA; Seiji Fujitsu General Limited MATSUNAGA; Junichi Fujitsu General Limited ONODERA
Original assignee: Fujitsu General Ltd
Current assignee: Canon Inc
Priority date: 1997-07-25
Filing date: 1998-07-24
Publication date: 2000-06-21
Anticipated expiration: 2018-07-24
Also published as: US20050190301A1; US7321401B2; EP1011264A4; JPH1146312A; CA2297957C; TW401683B; DE69835890D1; AU742007B2; KR20010022230A; DE69835890T2; JP3697844B2; AU8357998A; EP1011264B1; WO1999005855A1; CA2297957A1; RU2216118C2; ES2272002T3; KR100538765B1

Abstract

A contour emphasizing circuit which comprises a contour pick-up unit 10 for picking up a contour component HE from an input luminance signal Y, a level judging unit 15 for judging the luminance level of the input luminance signal Y, a coefficient control unit 17 for changing the coefficient in a plurality of steps depending upon a judgement signal and multiplying the contour component HE by the coefficient to output the product, and an adder 14 for adding the contour component outputted from the coefficient control unit 17 to the input luminance signal Y to output an emphasized-contour luminance signal. The coefficient to be multiplied by the contour component HE is changed in a plurality of steps depending upon the luminance level of the input luminance signal Y, and the contour component HE to be added to the input luminance signal Y is controlled to have a magnitude appropriate to the luminance level of the input luminance signal Y. As a result the contour is emphasized according to the luminance level of the input luminance signal Y without causing excessive contour emphasis by adding a large contour component to a dark image of a small luminance level, thus preventing formation of unnatural images.

Description

TECHNICAL FIELD

The present invention relates to a contour emphasizing circuit designed for sampling contour component from input video signal (e.g., digital input video signal), multiplying the sampled contour component by a coefficient (one of coefficients including 1) for contour emphasis, and adding the product thereof to the input video signal for outputting contour-emphasized video signal.

BACKGROUND OF THE INVENTION

The PDP (Plasma Display Panel) equipment using the plasma display panel and LCD (Liquid Crystal Display) equipment using the liquid crystal display panel as thin and lightweight display equipment have come to attract public attention. Such display equipment is conventionally of direct-drive type using digital video signal, wherein a contour emphasizing circuit, such as one shown in Fig. 1, is used for obtaining the contour-emphasized video signal from the input video signal.
The contour emphasizing circuit shown in Fig. 1 comprises a contour pick-up unit 10, a delay adjusting unit 12 and adder 14.
The contour pick-up unit 10 comprises one- dot delay units 18, 20 for sequentially delaying by one-dot the digital luminance signals (an example of video signal), which has been input to the input terminal 16, adder 22 for adding the luminance signal Y input to the input terminal 16 to the output signal from the one-dot terminal 16 to obtain the sum, multiplier 26 for multiplying the sum by coefficient 1/4 for outputting the product thereof, a multiplier 26 for multiplying the output signal from the one-dot delay unit 18 by coefficient 1/2 for outputting the product thereof, and a subtracter 28 for subtracting the output signal of the multiplier 24 from the output signal of the multiplier 26; wherein the contour component (i.e., high-pass component) HE in horizontal direction of reference picture element are sampled, for output, from the picture elements on the left side and right side (preceding and subsequent picture elements on time basis) of the reference picture element.
A delay adjusting unit 12 is designed for adjusting the timing for the input of the luminance signal, which has been input to the input terminal 16, to the adder 14 to the timing for the input of the contour component HE, which has been sampled by contour pick-up unit 10, to the adder 14 by delaying the output of luminance signal Y, which has been input to the input terminal 16, for a predetermined time interval.
The adder 14 adds the luminance signal Y, which is output from the delay adjusting unit 12, to the contour component HE, which is sampled the contour pick-up unit 10, to output the sum (Y + HE), as a contour-emphasized component, to an output terminal 30.
However, the contour emphasizing circuit shown in Fig. 1 has a problem as is described below because of being designed so that the contour component HE sampled by the contour pick-up unit 10 is directly output to the adder 14 regardless of the luminance level of the luminance signal Y input to the input terminal 16 is high or low.
The problem is that unnatural picture having overemphasized contour is produced if a contour component having too high a value is added to a relatively dark picture of a low luminance level. Another problem of the circuit is that the contour cannot be emphasized sufficiently if a contour component having to low a value is added to a bright picture having a high luminance level.
The present invention is designed for the purposes of solving the above problems and for providing a contour emphasizing circuit capable of accomplishing contour emphasis matching the luminance level of input video signal.

DISCLOSURE OF THE INVENTION

The contour emphasizing circuit according to the present invention is characterized by comprising a contour pick-up unit for sampling contour component from input video signal, a luminance level judging unit for discriminating the luminance level of input video signal, a coefficient control unit for not only selectively changing coefficient among a plurality of coefficients according to the judging signal from the luminance level judging unit but also multiplying the contour component sampled by means of a contour pick-up unit by a selected coefficient for the outputting the product thereof and an adder for adding the contour component output from the coefficient control unit to input video signal for outputting contour-emphasized video signal.
A coefficient is selected from among a plurality of coefficients, so that a plurality of coefficients are available for being multiplied by the contour component according to the luminance level of the input video signal. Thus, the picture can be prevented from becoming unnatural picture by controlling the contour component to be added to the input video signal to a value matching the luminance level of the input video signal.
Further, the level judging unit may comprise a decoder for discriminating the luminance level of the input video signal from n number (n = 2 and integers) of luminance levels, and the coefficient control unit may comprise n number of multipliers for multiplying the contour component, which is sampled by means of the contour pick-up unit, by the coefficient corresponding to each luminance level among n number of luminance levels for outputting the product thereof, number of AND gates using, as the gate control signal, the signal interpreted by the decoders connected respectively to the output sides of the n number of multipliers and an OR gate connected to the output sides of the n number of the AND gates. By doing so, the level judging unit and the coefficient control unit can be formed easily.
Further, the level judging unit may comprise a decoder capable of discriminating each of 4 luminance levels of input video signal, and the coefficient control unit may comprise 4 multipliers for multiplying the contour component, which is sampled by the contour pick-up unit, by one of the coefficients 1/8, 1/4, 1/2 and 1 for outputting the product thereof, 4 AND gates respectively connected to the output sides of the 4 multipliers for using, as the gate control signal, the signal interpreted by the decoders respectively connected, and an OR gate connected to the output side of the 4 AND gates. By doing so, the level judging unit and the coefficient control unit can be formed more easily.
Further, the composition of the contour pick-up unit can be simplified by composing the contour pick-up unit with a horizontal contour component pick-up unit designed for sampling the contour component in horizontal direction from input video signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram showing an example of conventional contour emphasizing circuit.
Fig. 2 is a block diagram showing an embodiment of the contour emphasizing circuit according to the present invention.
Fig. 3 is a block diagram showing examples of the level judging unit and the coefficient control unit shown in Fig. 2.

BEST MODES FOR CARRYING OUT THE PRESENT INVENTION

The content of the present invention will be described in detail referring to the accompanying drawings.
Fig. 2 shows a contour emphasizing circuit as an embodiment of the present invention, wherein common reference numerals are assigned to those parts common to those shown in Fig. 1.
In Fig. 2, numeral 10 denotes the contour pick-up unit; 12,13, the delay adjusting unit; 14, an adder; 15, the level judging unit; 17, coefficient control unit.
The contour pick-up unit 10 comprises one- dot delay units 18, 20 for sequentially delaying by 1 dot the digital luminance signals (an example of video signal), which has been input to the input terminal 16, adder 22 for adding the luminance signal Y input to the input terminal 16 to the output signal from the one-dot terminal 16 to obtain the sum, multiplier 26 for multiplying the sum by coefficient 1/4 for outputting the product thereof, and subtracter 28 for subtracting the output signal of the multiplier 24 from the output signal of the multiplier 26; wherein the contour components HE in horizontal direction are sampled, for output, from the picture elements on the left side and right side of the reference picture element.
The level judging unit 15 is designed to discriminate the luminance level of the luminance signal Y input to said input terminal 16 and output a corresponding judging signal. More specifically, as shown in Fig.3,(the level judging unit 15) comprises the decoder 32 for decoding the luminance level of the luminance signal Y with reference to the values of the upper 3 bits
of the 8-bit luminance signal Y. That is, the decoder 32 outputs a signal (e.g., H-level signal) corresponding to the output sides 1 ○ , 2 ○ , 3 ○ and 4 ○ depending on whether the values of the upper 3 bits of the luminance signal Y input to the input terminal 16 correspond to which of [000], [001], [010∼011] and [100∼111], thereby interpreting whether the luminance level of the luminance signal Y corresponds to which of the hexadecimal numbers of 4 levels, namely, [00∼1F], [20∼3F], [40∼7F] and [80∼FF].
The coefficient control unit 17 is designed for selectively changing the coefficient according to the judging signal output from the level judging unit 15 by way of the delay adjusting unit 13, as well as for multiplying the contour component sampled by means of the contour pick-up unit 10 by this coefficient for outputting the product thereof. More specifically, as shown in Fig. 3,(the coefficient control unit 17) comprises the four multipliers 36₁, 36₂, 36₃ and 36₄ for selectively multiplying the contour component HE, which has been sampled by said contour pick-up unit 10 and input by way of the input terminal 34, by the coefficients 1/8, 1/4, 1/2 and 1 for outputting of the product thereof, four AND gates, 38₁, 38₂, 38₃ and 38₄ respectively connected to the output sides of the four multipliers 36₁, 36₂, 36₃ and 36₄ for using the signal decoded by the decoder 32 as gate control signal, and the OR gate 40 connected to the output sides of the four AND gates, 38₁, 38₂, 38₃ and 38₄; wherein the contour component is output to the adder 14 from the OR gate by way of the output terminal 42. Further, in Fig. 3, for the simplicity of illustration, the delay adjusting unit 13 interposed between the decoder 32 and the coefficient control unit 17 is omitted; as the result, in the diagram, the output terminals 1 ○, 2 ○, 3 ○ and 4 ○ are shown as if the signals were directly input to the AND gates 38₁, 38₂, 38₃ and 38₄.
The delay adjusting unit 13 delays for a predetermined time interval the output of the judging signal from the level judging unit 15 in order to respectively adjust the timing for outputting to the coefficient control unit 17 the contour component HE sampled from the input luminance signal by the contour pick-up unit 10 and the timing for inputting to the coefficient control unit 17 the judging signal from the level judging unit 15.
The adder 14 adds the luminance signal Y, which has been input to the input terminal 16 and delayed for a predetermined time interval by the delay adjusting unit 12, to the contour component output from the coefficient control unit 17 for outputting the sum to the output terminal 30 as a contour-emphasized luminance signal.
The delay adjusting unit 12 delays the output of the luminance signal Y, which has been input to the input terminal 16, for a predetermined time interval in oder to respectively adjust the timing for the input of the luminance signal, which has been input to the input terminal 16, to the adder 14 and the timing for the input of the contour component, which has been output from the coefficient control unit 17, to the adder 14.
Next, the functions of the parts shown in Fig. 2 will be explained referring to Fig. 3 too.
(1) The contour component HE is sampled from the 8-bit luminance signal, which has been input to the input terminal 16, by the contour pick-up unit 10, and the sampled contour component HE is input to the coefficient control unit 17.
(2) In Fig. 3, the decoder 32 and the coefficient control unit 17 respectively function as described in (a),(b),(c) and (d) below depending on whether the luminance level of the 8-bit signal input to the input terminal 16 corresponds to which of the four levels,i.e.,[00∼1F] (hexadecimal number; the same applies hereinafter), [20∼3F], [40∼7F] and [80∼FF].
(a) Case where the luminance level of luminance signal Y is [00∼1F]: The decoder 32 interprets that the luminance level is [00∼1F] on the basis of that the values of upper 3 bits of the luminance signal Y is [000], thereby outputting an H-level signal from output side 1 ○. This output signal is delayed for a predetermined time interval by the delay adjusting unit 13 (not shown in Fig. 3) and input to the AND gate 38₁ for the electrification (i.e., being kept open) thereof. In this condition, L-level signals are output from the output sides 2 ○ though 4 ○ of the decoder 32, so that other AND gates 38₂ through 38₄ are kept unelectrified (i.e., being kept closed).When the AND gate 38₁ is electrified, the contour component (HE/8) multiplied by 1/8 by means of the multiplier 36₁ is input to the adder 14 by way of the AND gate 38₁, OR gate 40 and output terminal 42.
(b) Case where the luminance level of luminance signal Y is [20∼3F]: The decoder 32 interprets that the luminance level is [20∼3F] on the basis of that the values of upper 3 bits of the luminance signal Y are [001] and outputs an H-level signal from the output side 2 ○. This output signal is delayed for a predetermined time interval by means of the delay adjusting unit 13 and input to the AND gate 38₂ for the electrification thereof.When the AND gate 38₂ is electrified, the contour component (HE/4), which has been multiplied by 1/4 by multiplier 36₂, is input to the adder 14 by way of the AND gate 38₂, OR gate 40 and output terminal 42.
(c) Case where the luminance level of luminance signal Y is [40∼7F]: The decoder 32 interprets that the luminance level is [40∼7F] on the basis of that the values of upper 3 bits are [010∼011] and outputs an H-level signal from the output side 3 ○. This output signal is delayed for a predetermined time interval by means of the delay adjusting unit 13 and input to the AND gate 38₃ for the electrification thereof.When the AND gate 38₃ is electrified, the contour component (HE/2) multiplied by 1/2 by means of the multiplier 36₃ is input to the adder 14 through the AND gate 38₃, OR gate 40 and output terminal 42.
(d) Case where the luminance level of luminance signal Y is [40∼7F]: The decoder 32 interprets that the luminance level is [40∼7F] on the basis of that the values of upper 3 bits are [010∼011] and outputs an H-level signal from the output side 4 ○. This output signal is delayed for a predetermined time interval by means of the delay adjusting unit 13 and input to the AND gate 38₄ for the electrification thereof.When the AND gate 38₄ is electrified, the contour component (HE) multiplied by 1 by means of the multiplier 36₄ is input to the adder 14 through the AND gate 38₄, OR gate 40 and output terminal 42.
(3) In Fig. 2, the adder 14 adds the contour component output from the coefficient control unit 17 to the luminance signal Y, which has been input to terminal 16 and delayed for a predetermined time interval by the delay adjusting unit, to output the sum to the output terminal 30 as a contour-emphasized luminance signal.
For instance, when the luminance level of the luminance signal is [00∼1F], contour component (HE/8) is added to the luminance signal Y, and the sum (Y + HE/8) as a contour-emphasized luminance signal is output to the output terminal 30. Further, when the luminance level of the luminance signal Y are [20∼3F], [40∼7F] or [80∼FF], contour component (HE/4), (HE/2) or (HE) is added to the luminance signal Y, and sum (Y + HE/4), (Y + HE/2) or (Y + HE) as a contour-emphasized luminance signal is output to the output terminal 30. Thus, contour emphasis matching the luminance level of luminance signal Y is available.
The embodiment described above relates to a case where the contour pick-up unit comprises a horizontal contour pick-up unit for sampling the contour component in horizontal direction from the input video signal, but the present invention is not limited to this embodiment but is also applicable to other contour pick-up units as long as they are designed to sample the contour component from input video signal. For example, the present invention is applicable to the case where a contour pick-up unit comprises a vertical contour pick-up unit designed for sampling the contour component in vertical direction or to the case where a contour pick-up unit comprises a horizontal-vertical contour pick-up unit designed for sampling the contour component in both the horizontal and vertical directions.
The embodiment described above relates to a case where the level judging unit comprises a decoder for interpreting whether the luminance level of an input video signal corresponds to which of four luminance levels, and a coefficient control unit comprises four multipliers for multiplying the contour component sampled by means of
the contour pick-up unit by any of coefficients 1/8, 1/4, 1/2 and 1 for the output of respective products, four AND gates respectively connected to the output sides of the four multipliers for using the signal interpreted by the decoder as gate signal and an OR gate connected to the output sides of the four AND gates, but the present invention is not limited to this embodiment. For example, the present invention is also applicable to a case where the level judging unit comprises a decoder for interpreting whether the luminance level of a input video signal corresponds to which of n number (n = 2 or larger integers) of levels, and coefficient control unit comprises n number of multipliers for multiplying the contour component sampled by means of the contour pick-up unit by a corresponding coefficient for outputting the product thereof, a number of AND gates respectively connected to the output sides of the n number of multipliers for using, as gate control signal, the signals interpreted by a decoder, and an OR gate connected to the output sides of the n number of AND gates.
The embodiment described above relates to a case where the level judging unit comprises a decoder, and the coefficient control unit comprises multipliers, AND gates and OR gate, but the present invention is not limited to this embodiment but applicable also to the case where the level judging unit may be anything capable of discriminating the luminance level of input video signal, and the coefficient control unit may be anything capable of selectively changing the coefficient according to the judging signal from the level judging unit, as well as for multiplying the contour component sampled by means of the contour pick-up unit by a corresponding coefficient for the output of the product thereof.

INDUSTRIAL APPLICABILITY

As described in the foregoing, the present invention relates to a contour emphasizing circuit designed for sampling contour component from input video signal, multiplying the sampled contour component by a contour emphasizing coefficient, adding the product thereof to the input video signal and outputting a contour-emphasized video signal, whereby the contour can be emphasized matching with the luminance level of the input video signal. Thus, the present invention can be used for preventing production of unnatural picture either by overemphasizing the contour of a dark picture having a low luminance level by excessively adding contour component or by under emphasizing the contour of a bright picture having a high luminance level by adding insufficient contour component.

Claims

A contour emphasizing circuit comprising a contour pick-up unit for sampling contour component from input video signal, a level judging unit for discriminating the luminance level of said input video signal, a coefficient control unit for selectively changing coefficient according to judging signal from the level judging unit and multiplying the contour component sampled by using said contour pick-up unit by the selected coefficient to output the product thereof, and an adder for adding the contour component output from the coefficient control unit to said input video signal to output the sum as a contour-emphasized video signal.
A contour emphasizing circuit according to claim 1, wherein the level judging unit comprises a decoder for interpreting whether the luminance level of the input video signal corresponds to which of n number (n = 2 or larger integers) of luminance levels, and the coefficient control unit comprises n number of multipliers for multiplying the contour component sampled by using the contour pick-up unit by the coefficient corresponding to one of said n number of luminance levels for outputting the product thereof, n number of AND gates respectively connected to the output sides of the n number of multipliers for using the signal interpreted by said decoder as gate control signal, and an OR gate connected to the output sides of the n number of AND gates.
A contour emphasizing circuit according to claim 2, wherein the level judging unit comprises the decoder for interpreting whether the luminance level of input video signal corresponds to which of four luminance levels, and the coefficient control unit comprises four multipliers for multiplying the contour components sampled by using the contour pick-up unit by any of coefficients 1/8, 1/4, 1/2 and 1 for outputting the product thereof, four AND gates respectively connected to the output sides of the four multipliers for using the signal interpreted by said decoder as gate control signal, the OR gate connected to the output sides of the four AND gates.
A contour emphasizing circuit according to claim 1, 2 or 3, wherein the contour pick-up unit comprises a horizontal contour component pick-up unit for sampling the contour component in horizontal direction from input video signal.